Rocks formed approximately 400 million years ago during the Silurian age are usually nested deep within the current outer layer of the earth. Surfacing in what has become the suburb of Deakin in Canberra, this anticline is a distinctive feature of the last marine incursion into the ACT region and is made up of predominantly sedimentary calcareous and tuffaceous mudstone or siltstone with some beds of limestone and quartz sandstone. The Deakin Anticline is a manifestation of ancient crustal forces exposed by quarrying during the late 1940s and early 1950s by workers for the Commonwealth Brick Works nearby.